Multisensor Inspection: Assessing the Condition of Large Diameter Pipes with 3D Digital Modelling

For the inspection of large diameter pipes, particularly wastewater and stormwater systems, closed-circuit television (CCTV) is the commonly chosen inspection method. However, the long-term management of critical pipe infrastructure requires intelligent decisions made with detailed and quantitative data that CCTV cannot provide. With newly developed multisensor inspection (MSI) technologies, it is now possible to quantify the shape and size of pipes, and defects within them, in three dimensions (3D). Advancements in MSI methods allow for measurement of remaining wall thickness, detection of voids developing outside the pipe, and the creation of 3D digital point clouds with millimeter accuracy. By using these quantifiable measurements, a more accurate assessment of large water, wastewater, and stormwater pipes can be obtained, allowing the pipeline owner to accurately estimate remaining service life via these predictive models. Advancements in MSI technologies are highlighted in this paper, including 3D LiDAR, sonar, and pipe penetrating radar (PPR), and how to combine these technologies to collect comprehensive, quantitative data from large diameter pipes. Benefits of the technology will be demonstrated by recent case studies. The owner of a large, critical, and irregularly shaped sewer tunnel in Denver, Colorado, needed accurate dimensions in order to undertake the needed rehabilitation. The 7,580 ft long tunnel was inspected using multiple LiDAR devices, sonar, and a high-definition 360-degree CCTV camera deployed on a custom-built long-range inspection platform. This combination of sensors provided a detailed, accurate, and comprehensive report that was critical for an effective rehabilitation plan. The second case study illustrates how Melbourne, Australia, used a robotic, multisensor crawler to inspect critical sewer lines in the 23.5 to 37.5-in. range. These reinforced concrete pipes were inspected with pipe penetrating radar, LiDAR, and high-definition CCTV camera in order to design an effective asset management plan. The effectiveness, adaptability, and affordability of the described technologies allow asset managers to obtain comprehensive and actionable data that in turn are essential for effective asset management.